1. Field of the Invention
The present invention relates to routing a received Signaling System 7 (SS7) message in a Common Channel Interoffice Signaling (CCIS) network of a out-of-band telecommunications system.
2. Description of the Related Art
Common Channel Interoffice Signaling (CCIS) networks provide out of band signaling for telecommunications networks such as public switched telephone networks. Most of the signaling communications for telephone networks utilize Signaling System 7 (SS7) protocol. An exemplary SS7 compliant CCIS network includes Service Switching Points (SSPs) (i.e., an SS7 capable telephony switch), Signaling Transfer Points (STPs), and data links between the STPs and SSPs and various telephone switching offices of the network.
As recognized in the art, the hardware and software operations of the SS7 protocol are divided into “layers”, similar to the Open Systems Interconnect (OSI) Network Model specified by the International Standards Organization (ISO). The “lowest levels” of the SS7 protocol include the Message Transfer Part (MTP) Level 1, Level 2, and Level 3. MTP Level 1 and Level 2 are equivalent to the OSI Physical Layer and the OSI Data Link layer, respectively. MTP Level 3, equivalentto the OSI NetworkLayer, provides message routing between signaling points in the SS7 network, and re-routes traffic away from failed links and signaling points and controls traffic when congestion occurs.
SS7 messages (also referred to as signal units) are routed throughout the SS7 network based on point codes specified within the SS7 message. In particular, each node of the signaling network is assigned a prescribed point code for purposes of addressing signaling messages throughout the SS7 network. The point code includes components that represent a network hierarchy based on the protocol being deployed.
One type of signal unit, known as a Message Signal Unit (MSU), includes a routing label which allows an originating signaling point to send information to a destination signaling point across the network. The routing label includes an originating point code (OPC) specifying the originating signaling node, a destination point code (DPC) specifying the destination for the SS7 messaging packet, and a signaling link selection (SLS) field. Hence, the selection of outgoing link is based on information in the DPC and SLS.
The size of the point code may vary depending on protocol; for example, each North American point code according to the American National Standards Institute (ANSI) uses 24 bits, whereas each point code specified by the International Telecommunication Union (ITU) uses 14 bits. In particular, an ANSI point code specifies a network hierarchy based on network, cluster, and member octets (e.g., 245-16-0 decimal). An octet is an 8-bit (i.e., 1-byte) value which can contain any value between zero and 255. Telcos with large networks have unique network identifiers while smaller operators are assigned a unique cluster number within networks 1 through 4 (e.g., 1-123-9). Network number 0 is not used; network number 255 is reserved for future use.
ITU-T point codes are pure binary numbers which may be stated in terms of zone, area/network, and signaling point identification numbers. For example, the point code 5557 (decimal) may be stated as 2-182-5 (binary 010 10110110 101).
The STPs are program controlled packet data switching systems. In operation, an STP will receive a packet data message from another node of the network, for example from an end office switching system. The STP analyzes the point code information in the packet and routes the packet according to a static routing table, also referred to as a translation table, stored within the STP. Any packet having a particular point code is output on a port going to the next CCIS signaling node specified by translation of that point code. Hence, the routing table stores for each (24-bit or 14-bit) point code a corresponding port address for outputting the packet to a specified linkset.
Once the STP selects the outbound linkset for the packet, the STP selects the outbound link for outputting the packet, for example using a round-robin scheme. In some cases, packets may be routed to a specific link within the linkset based on the SLS field: for example, even SLS field values may be mapped to one link of an outbound linkset, and odd SLS field values may be mapped to a second link of the outbound linkset.
The STP performs the same routing decision for received packets based on the respective point code information, regardless of packet type. Hence, the STP is unable to distinguish between different messages types, for example Integrated Services Digital Network User Part (ISDNUP) traffic, Signaling Connection Control Part (SCCP) traffic, and/or Transaction Capabilities Application Part (TCAP) traffic. Consequently, instances may arise where packets may be discarded due to congestion conditions. For example, an STP that receives a large amount of TCAP traffic destined for an outbound linkset having two links would evenly distribute the TCAP traffic across the two links; however, any additional SCCP traffic that was destined for the same outbound linkset could be discarded due to congestion encountered on the links on the outbound linkset.
Hence, there is a concern that a signaling node (e.g., a mobile switching center) is unable to distinguish between messages types, where high priority messages such as call setup messages may be adversely affected by less critical messages, such as Short Message Service (SMS) messages